DEFICITS AND RECOVERY OF FIRST-ORDER AND 2ND-ORDER MOTION PERCEPTION IN PATIENTS WITH UNILATERAL CORTICAL-LESIONS

Unilateral lesions in the posterior parietal cortex can degrade motion perception in the contralesional visual hemifield, Our aim was to inv estigate whether deficits caused by cortical lesions may be different for first-and second-order motion perception, and to study the time sc ale of any potential recovery. In nine patients with circumscribed les ions mainly in the parietal and fronto-parietal cortex, thresholds for direction discrimination were measured for stimuli presented peripher ally in their ipsi-and contralesional hemifield. Subjects had to ident ify the direction of a vertically moving object embedded in a backgrou nd of dynamic random dot noise. The object consisted of various propor tions of signal and noise dots. Signal dots were either (a) coherently moving in the same direction as the object (first-order), (b) station ary (second-order: drift-balanced), or (c) coherently moving in the op posite direction (second-order: theta). Noise dots were flickering. Tw o patients showed significant threshold elevations for all three types of motion stimuli presented in their contralesional hemifield, while thresholds for ipsilesional targets were unaffected. Neither showed an y selective deficit of first-versus second-order motion perception, bu t second-order motion was more impaired. Their lesions probably includ ed the motion area V5-MT, which was spared in the other seven patients . One of the patients, who was retested several times during a 27-mont h postlesional period, showed complete recovery for first-and second-o rder motion direction discrimination, as well as for the detection of speed differences.